Hydraulic pressure exchange pump



Aug. 11, 1959 L. P. DEACKOFF HYDRAULIC PRESSURE EXCHANGE PUMP 5 Sheets-Sheet l Filed April 6. 1956 INVENTORL L.. P- DEACKOFF W 6/: Arromvsv:

Aug. 11, 1959 P. DEACKOFF 7 2,898,866

HYDRAULIC PRESSURE EXCHANGE PUMP Filed April 6, 1956 5 Sheets-Sheet 2 INVENTOR. L. P. DEACKOFF bis Arron/ans Aug. 11, 1959 L. P. DEACKOFF 2,898,856

HYDRAULIC PRESSURE EXCHANGE PUMP Filed. April 6. 195a 5 Sheets-Sheet 3 INVENTOR. L. P. DEAC/(OFF luls ATTORNEYS L. P. DEACKOFF HYDRAULIC PRESSURE EXCHANGE PUMP Aug, 11, 1959 5 Sheets-Sheet 4 Filed April 6. '1956 IN VENTOR.

L.P. DEACKOFF 1 43. hzou m QM ATTORNEYS L. P. DEACKOFF 2,898,866

HYDRAULIC PRESSURE EXCHANGE PUMP Aug. 11, 1959" j Filed April 6. 195a 5 Sheets-Sheet 5 INVENT OR.

L. R DEACKOFF Z EiOU 7 his Armemsys States atent HYDRAULIC PRESSURE EXCHANGE PUMP Leon P. Deackolf, Watertown, Mass, assignor to Manton- Gaulin Manufacturing Company, Inc., Everett, Mass., a corporation of Massachusetts Application April 6, 1956, Serial No. 576,641

7 Claims. (Cl. 103-152) This invention relates to high pressure pumps, and more particularly to pumps of the hydraulic pressure exchange type in which a product fluid is pumped through the medium of a separate pumping fluid.

A primary object of the invention is to provide a pump capable of handling corrosive and erosive muds, slurries and solutions at high temperatures and/or pressures and at high capacities. It is a further purpose to provide a pump which can handle such product fluids far more effectively and economically than is possible through the use of conventional reciprocatory, rotary or centrifugal types. This is made possible by reason of the elimination of plungers, stuffing boxes, plunger packing, valves and other items common to the aforesaid more conventional pumps which require excessive maintenance when handling product fluids of an abrasive nature. An hydraulic pressure exchange pump of the type described herein overcomes these difliculties since the trouble-producing product fluid is never in contact with any closely spaced, relatively moving surfaces where the abrasive or corrosive nature of the product fluid can cause high rates of wear.

While pumps of the type to which this invention appertains employ a diaphragm or membrane to isolate the product fluid to be pumped from the pumping fluid and other parts of the system, they are not to be confused with the conventional reciprocatory diaphragm pump of relatively low capacity and pressure, working with a short stroke and producing widely pulsating discharge pressures. On the contrary, the pumps of this invention are capable of pumping capacities of almost any practical requirement, up to several hundred gallons per minute at pressures of over 1000 p.s.i. being readily obtainable, .for example, and the discharge pressure is uniform and steady. It is often very desirable to supply a fluid at .high pressure for processing, as to an autoclave, for ex- :ample, but because the maintenance of conventional pumps when handling abrasive materials is so uneconomical, compromise is usually made with respect to the operating pressure. With a pump such as here described, .it becomes unnecessary to accept this compromise.

The principle of hydraulic pressure exchange pumps of the type to which the invention is directed is generally well known. Basically, a nonerosive pumping fluid, such vas an hydraulic or lubricating oil, is transferred between .a reservoir and a pressure cylinder.

:stroke of the pumping cycle, hydraulic oil is pumped by a conventional pump from the reservoir into the cylin- -der, flexing the separating membrane and displacing the product fluid from its chamber and out through the discharge check Valve. On the suction stroke, the hydraulic 'oil is permitted to return freely to the reservoir through a by-pass, being displaced from the pressure cylinder by the product fluid under the aforesaid low pressure. In order to avoid the intermittent pumping action of this basic system, two or more pressure exchange cylinders and their associated pumping fluid systems are connected in tandem, so that while one is on the intake stroke, another is on its discharge stroke. By controlling the overlap of the operating cycles, the effect of output pressure changes in one pressure cylinder, during transition from pumping to intake strokes and vice versa, can be compensated for by another pressure cylinder. Wide pulsations from practically zero pressure to the maximum desired, as would occur in the single cylinder type, are thus avoided.

Notwithstanding the foregoing arrangement for staggering the pumping cycles of a number of pressure exchange cylinders, whereby the pressure pulsations are considerably reduced, prior pumps nevertheless are still subject in many instances to substantial pulsations which are objectionable for many reasons. One of the principal causes for these pulsations in prior equipment is due to hydraulic hammer in the transition from intake to discharge strokes in the several hydraulic pumping fluid systems.

It is accordingly an object of this invention to provide a practical pump which is remarkably free of appreciable pulsation, and wherein the discharge pressure is remarkably smooth and uniform at whatever setting is selected within the available operating range. To this end, pumps of the present invention employ relatively large pressure exchange cylinders and correspondingly slow rates of cycling. Furthermore, the cycling of these pressure exchange cylinders is accomplished by means of a novel pumping fluid control system, including the conduiting, valving and sequencing control of those valves, whereby any tendency toward hydraulic hammer is obviated and uniformity of the resultant discharge pressure is obtained in a much more eflicient and elfective manner than heretofore. This will be brought out more fully hereinafter in connection with the description of an embodiment of the invention illustrated in the accompanying drawings, wherein:

Fig. 1 is a flow diagram of a pressure exchange pump in accordance with the invention, the pump illustrated employing'two pressure exchange cylinders;

Figs. 2 and 3 are front and side elevational views, respectively, of the pressure exchange cylinders and associated product fluid check valves of the pump in Fig. 1;

Fig. 4 is an enlarged, fragmentary view in longitudinal section through one of the cylinders shown in Figs. 2 and 3;

Fig. 5 is a side elevational view, partly in section and on an enlarged scale of one of the product check valves shown in Figs. 2 and 3;

Fig. 6 is a diagrammatic representation of an air operated valve and solenoid operated pneumatic control valve of the type employed in the invention;

Figs. 7, 8 and 9 are top plan, side and end elevational views, respectively, of the hydraulic pumping fluid system and control cabinet; and

Fig. 10 is a schematic wiring diagram of the control circuit.

Referring to the flow diagnam of Fig. 1, the hydraulic pressure exchange pump comprises two pressure exchange cylinders 20, 20. As previously mentioned and as will appear more fully hereinafter, each of these cylinders is provided with a flexible membrane or diaphragm dividing their respective interiors into a pumping fluid chamber and a product fluid chamber. The latter is connected in each case by suitable conduits 22, 22', respectively, to check valve assemblies 24, 24'. These in tiirn are joined by common ihletand discharge manifolds 26, 28, respectively. The aforesaid pumping fluid chamber. of each cylindenis connected to separate pumping fluidisyst'e ms by suitable coiiduiti ng. Inasmuch as these areidentic al, the'descriptionbfone will sufhce here, it being understood that corresponding components of the other system, are designated by 'a prime on the respective reference numerals. y

High pressure'conduit 30 connects the pumping fluid chamber of cylinder 20 to the discharge of a positive displacement rotary pump 32. The latter is supplied with n hydraulic or lubricating oil through janintake pipe 34 from a reservoir'36. As will appear presently, pump 32 and'its counterpart 32"are connectedto a common shaft and driven continuously by a single motor so that each is contantly pumping fluid at its discharge port whenever the system is in operation. A check valye 38 is connected into the high pressure piping 30 bet ween the pump 32 and cylinder 20, thisfvalvebeing :a rranged to limit flow of the hydraulic pumping fluid from the pump toward the cylinder. At either side of valve 38, by-pass or return lines 40,j42 are likewise teed into conduit 30 and these lines both discharge backinto reservoir 36. By-pass lines 40 and 42 are provided with fluid motor operated return valves 44,. 46, respectively.

These valves are biased to a normally closed p'osition and are opened by a fluid motor device 60. Thisis operated by pneumatic "or hydraulic pressurejeg. compressed air, Water or oil, acting on the operating piston or diaphragm of the motor device of the respective .valves. An additional by-pass line 48 is teed into the high pressure pipe 30 between pump '32 and check valve 38, and is provided with a, manually operable valve 50.. Fluid motor operated valves 44, 46, are operated cyclically, as will be described'presently, to produce a reciprocating flow of hydraulic pumping fluid to and .identical arrangement is used for each of the other return valves 44f, 46 and 46'. As mentioned above, valve 44 is normally biased to closed position by suitable spring jmeans and the valve rod 56 is secured to the diaphragm 58 of the fluid'motor device 60. In the example specifically illustrated in the drawings, the fluid is assumed to be air and this is delivered under pressure to fluid motor device 60 through conduit 62 from'a three-way solenoid operated metering or control valve 64 of conventional construction. A supply line 66, having a manually set metering or restricting valve 68, therein, delivers compressed air to control valve 64 from a storage tank. Admission of air into line 62 from control valve 64 is normally blocked by a balanced plunger 70'which reciprocates within the.control valve. Upon'energization of solenoid 72, piston 70 is moved to positionto permit air to flow through line 62 into the operating chamber of fluid motor device 60 and thuso'pen valve 44. The rate at which air enters, and thus therate at which valve 44 is actuated, is controllable by means of the metering valve 68 in the supply line 66. Upon 1' deenergization of solenoid 72, piston 70 is returned to its original position by spring means, and air in fluid :motor device 60'is bled off to atmosphere through an ad ustable bleed orifice 74 in control valve 64.

from cylinder 20 in order to eflect the pumping of the in accordance'with the pressures on either side of its wall.

:93 to the 'controlj draulic pumping fiuid system pedestal'76 (Fig. 8).

is transferredto b I "bag 90. At'fthe lower-end, a sitn1lar'a'r'rangement (not "'shownyis provided exeept that thereisno axial passage assembly centrally 4 "drives, through conventional V-belt and pulley means 80, a shaft 81 which serves as a common drive shaft for both pumps 32, 32'. Control cabinet 82 houses the various electrical controls for the pump and is likewise mounted on the base.

Details of the construction of the pressure exchange cylinders are shown in Figs. Zthrough 5. The size of these cylinders determines the displacementcapacity of the system on each pumping stroke and consequently they may be quitejlarge. For a'unit having'aeapacity of g.p.m. at discharge pressures up to 20OOYp.s.i. for example, each cylinder is approximately 7 feet long and has "an 'i'rls'ide' diameter of 7 /2'to 8 inches. Referring to Figs. 2 and 5, cylinders20, 20' are'mounted upon a base 83 in side-by-side relation. Also mounted on the base are the respective product fluid check valve assemblies 24, 24', which are interconnected by the inlet manifold 26 and theldischarge manifold28. Each check valve assembly 24, '24, is likewise connected through conduits 22, 22 (Fig. 3) to thebase of ther'espective pressure exchange cylinders. At the upper'en'ds of'the cylinders, the hydraulic pumping fluid *co'n'duits 30, 30', are connected into the cylinders through suitable pipe Ts to which pressure gauge lines are "also run from gauges 84, '84. Each of the'c ylin'dersis provided with an automatic, float type'a'ir vent" 85,'-85, and manually controlled vents'86, '86. system indicatin'g panel P is suspended from the cylindersfthis par'iel being electrically eonnected v through suitable -m'ulticonductor cabling circu'its in"controlpanel' 82 on the by- In Fig. 4 the interior construction offfone of the pressure exchangefcylinders. 'isfillustra'ted. This 'c'o'r'isists 'of a high pressure cy'lindri cal;jouter'shell" 87 having'end caps SSb olted' to'it. Shell M med nneughout with :a neoprene sleeve 89. At'the' sf thesleeve is squeezed between the respfectiveen caps 88'and tlie-shell where it servesas 'a gasket. siispefided witliin the'cylinder is a diaphragm bag assembly 90 which in thisi'nst'ance' is generally cylindrical, beingfinly soitiewh'at shorter in length and'slightly smaller in" diameter than the interior of the cylinder. The bag is'pr'efEraBIy"constructedof "fabric 'reinforcednoprenesheet material a'nd is quite flexible. .At itsupperferid," this hag assembly'is clamped by' means of"ba 'nds' 92 "to"a cylindricalmetal plug or top holder 94 which isaiperthred topermitpassagetherethrough the botthm plug. The're 'is thus provided an enclosed hydraulic phinpihg fluidbharhber which serves rounds the' bag cylinder 20. D 'ue'to the'flexibility ofbag "90, this "'r'eadily collapses' and expands of the walls "In' order to facilitata such flexing" ofthe bag without subjecting it to"st'rain,.'the lower bag"holder or plug carries atube which projects a'xially"upwardly Within the bag and"telesc'opes about a downwardly projecting axial' tube "96- constituting a continuation of the 'con d'uitllill. Tube" 96 is provided i r'lt'rn'ally With perforations 98' to permit "transfer of' pumping :fluid to and from the bag 90. These perforations areloc'ated abet/ the lo er"teles'coping tube" and' arenot interfered with the course of slig ht axial shifting of'the' t'wo tubes which takes place during a" pumping cycle. 'This telescoping arrangement helps toimai ntain the diaphragm bag located in the pressure cylinder.

Vent tubes 98, 100, at the upper end of cylinder 20 lead to the automatic and manual air bleed valves 85, '86,.Ires'pectively. At the lower 'end ofthe cylinder 20,

" a drain'tube 102 is also provided and this is normally closed by a suitable valve, not shown.

Details of one of the product fluid check valves 24 are shown in Fig. 5. This is of relatively standard high pressure construction employing ball checks 104, 106, at the inlet and discharge sides, respectively, of conduit 22 which leads to the interior of the cylinder 20.

Description of the pumping cycle The operating sequence of the pump takes place as follows. Assuming that the motor 78 is running and pumps 32, 32, are delivering hydraulic pumping fluid, and further that the reservoir 36 is filled to a point where its high level switch 54 has been actuated, i.e., closed, while reservoir 36' is at its low level limit and switch 52 thereof has been closed, valves 44, 46, are closed, while valves 44', 46, are open. It is also assumed that the manually controlled pump by-pass valves 50, 50', are closed. At this point, diaphragm bag 90 of cylinder 26 is fully collapsed and the cylinder around the bag is filled with product fluid which has been delivered under low pressure from inlet manifold 26 through check valve 24. At this same time, the corresponding diaphragm bag 90' in cylinder 20' is fully expanded and most of the product fluid has been displaced from this cylinder by the expanded bag. Cylinder 20 is thus ready to start its discharge stroke while cylinder 20 is beginning its intake stroke.

Pump 32 delivers oil from reservoir 36 into cylinder 20, displacing the product through its product check valve 24 and delivering it under pressure to manifold 28. Pump 32 of course continues to deliver hydraulic pumping fluid but since the pump return valve 44' is open, this fluid is diverted back into the reservoir through by-pass line 40. Also since the cylinder return valve 46 is now open, pumping fluid in the expanded diaphragm bag 90' of cylinder 20 is displaced by collapse of this bag owing to product fluid coming in through check valve 24 under a low head. Check valves 38, 38 at all times prevent any reverse flow of fluid to their respective pumps from the diaphragm bags.

At the end of the pumping stroke of cylinder 20, the low level switch 52 in reservoir 36 is closed. When this occurs valves 44, 46, open and valve 44 closes. At this point, reservoir 36 should now be filled to a point where its high level switch 54 has been closed, and this will act to close cylinder return valve 46'. No more hydraulic pumping fluid can therefore be expelled from cylinder 20. In case high level switch 54' was not actuated and valve 46' did not close, an interlocking circuit in the electrical control system is energized and a no delivery condition exists at the discharge manifold 28 until switch 54 closes valve 46. Assuming however that the system is operating properly and that the level in reservoir 36 has now reached its upper limit, pump 32' now begins to deliver hydraulic fluid to its cylinder 20' and product fluid continues to discharge under pressure at manifold 28.

Since valves 44, 46 have now been opened, fluid delivered by pump 32 is by-passed through pump by-pass line 40 and pumping fluid previously delivered to cylinder 20 is returned to reservoir 36 through by-pass line 42, being displaced from cylinder 20 by the incoming product fluid. When pump 32' has reduced the level of fluid in reservoir 36 to a point where the low limit switch 52 is closed, valves 44, 46' are opened and valve 44 of the alternate system is closed. Assuming that the fluid returned to reservoir 36 has reached the proper high level and actuated switch 54, valve 46 closes. One complete pumping cycle has now been completed. Again, however, if the level in reservoir 36 failed to rise to the proper point, valve 46 is not closed and a no delivery condition exists until that valve does close. As will be explained presently, provision is made to give a warning signal to a pump operator should such condition arise.

The manually controlled by-pass valves 51), 50' are adjustable to vary the pump output capacity at manifold 28 within the design limits of the equipment. It will be noted that the stroke of the pump is not affected by the adjustment of valves 50, 50'. The stroke is equal to the quantity of oil between the low and high levels in reservoirs 36, 36. This is easily adjustable by varying the setting of the low and high level switches 52, 52, 54, 54. The maximum volume of the stroke is of course governed by the design of the pressure cylinder.

By properly controlling the sequence of operation of valves 44, 44', 46, 46, the discharge pressure at manifold 28 may be kept uniformly steady while the system is in operation. As has previously been mentioned, these valves are spring biased to a normally closed position and are moved to an open position by fluid motor means under the control of a control valve 64, the rate of operation of these valves is vital in eliminating hydraulic hammer. It is for this reason that the fluid metering provision previously described is supplied so as to permit control of the rate at which the actuating fluid is delivered to the operating diaphragms or pistons of the valve motor devices, or is bled oif therefrom.

Referring again to the diagram in Fig. l and to the description of an operating cycle of the pump just described, toward the end of the pumping stroke of cylin der 20, cylinder return valve 46 closes when high level switch 54 is actuated. The closing of valve 46 is not critical, therefore no restriction is used on the fluid outlet 74 of its associated three-Way solenoid valve 64. At this point in the cycle, valves 44, 46, are still closed. However, when low limit switch 52 of reservoir 36 is closed at the end of the pumping stroke, valves 44, 46, open at a previously determined speed, being controlled by the rate at which air or other fluid is admitted to their respective diaphragms through their respective three-way solenoid valves 64. In practice, valve 46 is made to open slightly faster than valve 44. This is essential so that check valve 38 does not slam shut. By opening valve 46 slightly faster than valve 44, the flow through valve 38 is decelerated at a controlled rate preventing this valve from slamming and causing hydraulic hammer. Valve 44' also closes during this phase of the cycle, its closing rate being restricted by the metering valve 68 of its associated control 64. This closing rate is balanced against the speed at which valves 44, 46 are opened. During the transition from one stroke to the other, therefore, hydraulic oil is pumped simultaneously for a short period of time from reservoir 36 and reservoir 36' into each of the respective pressure cylinders, and thus there is maintained a constant pressure of the product at the discharge manifold 28. As in the case of valve 46', the closing of the valve 46 at the end of the intake stroke is not critical and the rate is not controlled therefore.

The problems of getting smooth, uniform pressure discharge which exist at an output capacity of three gallons per minute, for example, are completely diiferent from those at 25 gallons per minute. At the latter capacity, a gradual transition such as is accomplished by the just described metering of the valve actuating fluid is essential and this becomes all the more vital at higher capacities such, for example, as 200 gallons per minute. The system just described makes it possible to attain capacities of this order Without the difliculties which have been inherent in previously known pressure exchange pumping systems.

Description of the electrical control cincuit Proper sequencing of valve operation as just described is accomplished by means of the electrical control circuit illustrated schematically in Fig. 10. This control circuit also serves to give adequate visual and aural warning of failures in the pumping system and to protect the hydraulic circuits from damage in the event foreign fluids work their way into the hydraulic system.

Referring to Fig. 10, the system consists basically of three mechanical latch relays 110, 112, 114. Relay 110,

7. when energized by low level' switch 52, opens valve 46 by energizing solenoid'72 of the respective pneumatic controlvalve 64. Relay112, when energized by low level limit switch 52', opens valve 46' by energizing the corresponding solenoid'72' of its pneumatic control valve. Relay 114, when energized by the low level switch 52, opens valve 44 and allows valve 44 to close; when energized by the corresponding low level switch 54' of the other system, relay 114 opens valve 44' and closes valve 44. Thus one or the other, but never both, 'of valves 44, 44', is always open.

In the-event that valves 46, 46', are open simultaneously (this will happen any time a reservoir fails to fill properly at the end of the intake stroke of its respective system) relays 116, 118, are simultaneously energized, completing a circuit from terminal 7 of a photoswitch 120 through the respective contacts 122, 124, to the ungrounded side of horn 126, sounding the horn to indicate no delivery. As soon as either valve 46 or 46' is closed, the horn will stop sounding; and when the .respective cylinder return valve 46, 46', on the side which'is onpumping stroke closes, pumping by that system will resume.

In the event that both low level switches 52, 52, are closed simultaneously, relays 128, 130, will *be simultaneously energized. These carry contacts132, 134, respectively, each set of which is in a circuit between the hot side 136 of the power mains and the ungrounded side of the operating coil of a pump motor control relay 138. Thus it will be seen that should both relays 128, 130 be energized simultaneously, breaking both power circuits to relay 138, the latter is deenergized; and interrupts the power to the pump motor 78 and motor push button circuit. This deenergizes the pump motor push button circuit, stopping all pumping. If this happens, it is necessary to restart the pump motor manually by depressing-the start button 140. I

The photoswitch level controller 120 contains a normally closed and a normally open contact. Probes 142, 142' (see Fig. 8) are placed in the respective'hydraulic pumping fluid reservoirs 36, 36', and so long as therprobes are not in contact with a conducting fluid, terminal 1 of the photoswitch 120 is hot providing .av power source for the pump motor push button circuit through control relay 138. However, when any of the probes comes in contact with a conducting liquid, terminal 3 of the photoswitch 120 becomes energized and terminal 1 becomes deenergized. In this condition a telltale? light 144 comes on and horn 126 sounds a warning. "Ihe horn will also be energized through this circuit for approximately 30 seconds after the control circuit is first energized by closing of relay 146 until the tube in the photoswitch 120 warms up and starts conducting, breaking the alarm circuit and energizing the motor push button circuit as previously described. Relay 146 is a single pole relay which simply holds the control system energized after the start push button 148 is depressed and until the stop button is pushed.

Telltale lights similar to probe lights 144 are associated with each of the high and low level pumping fluid switches 52, 52, 54, 54', as well as with each of the bypass valves 44, 44', 46, 46'. Additionally there-is a light indicating power delivered'to the control'circuit and one indicating operation of the pump 'mot0r,as'well as of energization of one of the probes 142 as previouslymentioned. To save complicating the wiring diagram, the return circuits to each of the several indicator lights is omitted but the circuitry is conventional and will be readily understood. Detailed explanation therefore is unnecessary. All of these lights areplaced on" the indicator panel P (Figs. 2 and 3) and are connected'to the control circuit by the multiconductor cable 93. The lights are appropriately positioned on the indicator 'panel inconjunction with a combined pump flow and electrical con- 'trol diagram similar to that in Fig. of the drawings, "whereby the 'pump operatoris'enabled to check the system readily for proper operation and to locate the difficulty quickly in case of malfunction.

What is claimed is: g

1. An hydraulic pressure exchange pump for a product fluid to be-pumped, comprising two pressure exchange cylinders having flexible diaphragms therein dividing each into product. fluid and pumping fluid chambers, respectively; a separate pumping fluid system connected to each of. the latter and a common product fluid system connected to the product fluid chambers of both cylinders; control means for operating said pumping fluid systems in tandem so that while one of said pressure cylinders is in its discharge stroke, the other is in its intake stroke; said product fluid system including inlet and discharge manifolds, and check valves operatively associated with each cylinder permitting product fluid under low pressure to enter the respective cylinders from said intake manifold during the intake stroke and to be displaced into said discharge manifold during discharge stroke, respectively, of the cylinders but preventing reverse flow in said manifolds; each of said separate pumping fluid systems being identical and including a fluid reservoir, 21 positive displacement pump which delivers fluid therefrom continuously, a pump conduit connecting the pump output with the pumping fluid chamber of its respective cylinder, at check valve in said conduit limiting flow in a direction toward said chamber, return lines connected into said pump conduit at either side of said check valve and leading back to the reservoir, one of said return lines constituting a pump by-pass and having a normally closed pump return valve therein, the other line constituting a cylinder return line and having a normally closed cylinder return valve therein; fluid motor means for actuating said return valves to open position; said pumping fluid control means including means responsive to predetermined high and low fluid levels in each reservoir; said low level responsive means in one reservoir being adapted, when the fluid level therein reaches the predetermined low level, to cause both said return valves in its system to open and the pump return valve of'the other pumping system to close; saidhigh level responsive means in said reservoirs being adapted, when the fluid level therein reaches the predetermined high level, to cause the cylinder return valve of the respective system to close; and fiuidmeter- 'ing means operatively associated with each of said fluid motor actuated return valves to regulate the speed of operation thereof, said metering means balancing the rate of opening of both return valves of a first system, as the latter approaches the end of its discharge stroke, with the rate of closing the pump return valve of the other system, as the latter starts its discharge stroke, so as to maintain a constant discharge pressure of the product'fluid, said metering means likewise retarding the rate of opening of the pump return valve of said first system with respect to the rate of opening of its associated cylinder return valve during transition from discharge to intake stroke in each system.

2. An hydraulic pressure exchange pump as defined in claim 1, wherein each of said pumping fluid systems includes a manually controlled by-pass valve in parallel with said fluid motor actuated pump return valve which is adjustable to set the product fluid discharge pressure of the pump.

3. An hydraulic pressure exchange pump as defined in claim 1, wherein said pumping fluid system pumps are driven simultaneously by a single electric motor.

4. An hydraulic pressure exchange pump as defined in claim 3, wherein said pumping fluid control means includes an electric circuit and a source of power for energizing said circuit, a'first relay operativelyassociated with each of said low level responsive means, respectively, and energized'by said power source whenever the fluid in said reservoirs is below the predetermined, low level, a pumpmotor control relay, each of said first relays having norm-ally closed contact points completing a circuit from said power source to said pump motor control relay independently of the other of said first relays when deenergized but breaking its respective circuit to said pump motor control relay when energized, whereby said latter relay is deenergized whenever the fluid level in both said reservoirs drops below said predetermined low level.

5. An hydraulic pressure exchange pump as defined in claim 4, which further includes an interlock relay operatively associated with each of said return valves and energized by said power source whenever the corresponding return valve is open, and a normally open interlock circuit including a warning device, said interlock relays being energized to close said interlock circuit and actuate said warning device whenever both of said return valves are open simultaneously as a result of incomplete filling of a reservoir on the intake stroke of its respective system.

6. An hydraulic pressure exchange pump as defined in claim 1, wherein said pumping fluid control means includes an electric circuit and a source of power for energizing said circuit, an interlock relay operatively associated with each of said return valves and energized by said circuit whenever the corresponding return valve is open, and a normally open interlock circuit including a warning device, said interlock relays being energized to close said interlock circuit and actuate said warning device whenever both of said return valves are open simultaneously as a result of incomplete filling of a reservoir on the intake stroke of its respective system.

7. An hydraulic pressure exchange pump as defined in claim 1, wherein said pumping fluid systems are driven simultaneously by a single electric motor and said pumping fluid control means includes an electric circuit, ineluding said pump motor, and a source of power for energizing said circuit; a latching relay for each pumping fluid system controlled by said high and low level responsive means in the respective system reservoirs, a

three-way solenoid operated control valve for each of said fluid motor operated return valves, said latching relays having latching and unlatching solenoids and normally open switch contacts controlled by said relay solenoids, said contacts being in circuit between said power source and the solenoids operated of the respective solenoid control valves, whereby fluid pressure is delivered to said return valves only when said latching relays are energized and latched, said low level responsive means in said reservoirs including switch means in circuit between said power source and the latching solenoid of the respective latching relay, said last switch means being closed to complete the circuit when the fluid in the respective reservoir reaches said predetermined low level; said control means also including a further latching relay having latching and unlatching solenoids, the latching solenoid of which is in electrical parallel with the latching solenoid of one of said first named latching relays and the unlatching solenoid is in electrical parallel with the latching solenoid of the other of said first named latching relays; a three-way solenoid operated control valve for each of said pump return valves, said further relay having switch contacts alternately connecting one or the other of the solenoids of said control valves to said power source; said high level responsive means including switch con tacts closed in response to fluid reaching said predetermined high level to complete a circuit to said power source through the unlatching solenoid of the respective first named latching relay.

References Cited in the file of this patent UNITED STATES PATENTS 

